Let me take a stab at it:

I think what they're saying is that in the past if you were redeeming a Delta SkyMiles award for travel to Europe (i.e., not an AF partner award obtained using SkyMiles but instead an honest-to-goodness Delta award using SkyMiles), you could book your flight using any Delta seat -- whether the seat was a seat on a real Delta jet or whether the seat was a Delta-coded seat on an Air France jet (assuming, of course, that award seats were available).

Under this new rule, if you're booking using a Delta award, you'll have to book it on Delta metal only. You won't be able to use a Delta award on Delta-blocked seats on Air France-operated flights, because Delta isn't going to dedicate any of its block of seats on those Air France flights to award travel.

So, if there are three flights to Paris from Atlanta (two on Delta and one on AF) and the AF flight suits your schedule better, you won't be able to redeem a Delta award on it (even though you can buy a Delta seat on that Air France flight using Delta-blocked seats). Instead, you'll have to redeem a SkyMiles Partner award (i.e., AF award using Delta SkyMiles) to fly on the Air France flight.

You'll still call Delta reservations (not Air France), but at the voice prompt you'll push the key for International Partner Awards rather than Delta awards.